1. Field of the Invention
The present invention relates generally to printers, and more particularly to a type carrier belt formed as a continuous endless loop and having interchangeable or replaceable type segments.
2. Description of the Prior Art
Modern printing apparatus such as chain printers, band printers and the like employ a chain or type carrier belt which is rotated about two drums, spools or pulleys. The chain or belt includes a plurality of printing elements each provided with an alpha-numeric character, and each of the individual type elements will move past the print station one time during each revolution of the chain or belt loop.
It has become common in the industry to utilize endless metallic or stainless steel print belts having the characters and timing marks affixed thereon by either mechanical, chemical or electrical generation. When the ends of such metal belts are welded together to form a continuous endless loop, the belts may warp or become out of line during use thus rendering them ineffective.
It is also common to construct non-metallic type carrier belts or chains where the character-bearing elements or segments are affixed to the flexible non-metallic belts by mechanical or chemical bonding techniques.
Many of the prior art type carrier belts are expensive to produce since it is extremely difficult to technically control the shape and contour of the belt, especially where the belts are required to have special teeth, projections, holes or notches on the belt or band portion itself.
In most of todays printers, the type carrier belt is stretched over two pulleys or drums, one pulley being driven to cause the belt to be rotatably driven at a relatively high velocity and the other pulley being spring-loaded to maintain a constant pressure on the belt. Every time a given type segment passes over a pulley, severe internal stresses are induced or generated within the belt itself often resulting in metal fatigue or failure thereby reducing the useful life of the belt.
It has also been found that most of the endless metallic belts and some of the non-metallic belts are designed primarily for use with pulleys having an outside diameter of 5 inches or more. As the pulley diameter decreases, the internal stresses within the driven belt increase very rapidly. This means that pulley sizes smaller than 5 inches outside diameter are not economically sound. This means that most of the equipment used today employs rather large cabinets or housings encompassing the machine. Therefore, the belts now utilized have several problems which limit the useful life of the belt itself and also the life of the characters on the belt regardless of how the characters are applied thereto.
Whatever solutions have been adopted heretofore to extend the life of the belt or of the characters thereon, they have not been economically or technically sound and the problems still exist. It has been found that some type segments or printing elements on the belt tend to wear more rapidly than others. In most of the systems of the prior art, the entire band or chain had to be replaced even if only a small portion or a few type segments had become worn. While a few attempts have been made to provide interchangeable type segments which can be easily attached to and removed from the carrier belt, most of these belts have suffered from type alignment problems, the inability to retain a desired pitch, and the inability to place the individual type segments close enough together in a side-by-side manner so as to eliminate the play between adjacent carrier segments.
The United States Patents which are considered to represent the current state of the prior art are as follows: Helms, U.S. Pat. No. 3,845,711, issued Nov. 5, 1974; Migoux et al, U.S. Pat. No. 3,844,211, issued Oct. 29, 1974; Deproux, U.S. Pat. No. 3,838,765, issued Oct. 1, 1974; Funk et al, U.S. Pat. No. 3,835,771, issued Sept. 17, 1974; Pittis, U.S. Pat. No. 3,826,191, issued July 30, 1974; Bowers et al, U.S. Pat. No. 3,805,698, issued Apr. 23, 1974; Hansen et al, U.S. Pat. No. 3,774,531, issued Nov. 27, 1973; Perry et at, U.S. Pat. No. 3,745,918 issued July 17, 1973; Huntoon et al, U.S. Pat. No. 3,742,848, issued July 3, 1973; Bossi, U.S. Pat. No. 3,741,110, issued June 26, 1973; Picard, U.S. Pat. No. 3,724,371, issued Apr. 3, 1973; Niccolai, U.S. Pat. No. 3,719,139, issued Mar. 6, 1973; and Harrington, U.S. Pat. No. 3,665,852, issued May 30, 1972.